Such a control circuit is regarded as known. A polarity reversal protection device suitable for this purpose is described in German Patent No. 39 24 499, in particular with respect to FIG. 4D given there. Using such a polarity reversal protection device for a d.c. motor powered with a battery voltage prevents a short circuit over the freewheeling diode and an inverse diode of a power MOSFET provided for clocked control of the d.c. motor in the event of reversal of polarity of the battery voltage. Furthermore, the polarity reversal protection device prevents destruction of an electrolytic capacitor provided in the control circuit in the event of polarity reversal. With a known control circuit, the polarity reversal protection device is connected to the lead wire or to the outgoing cable of the motor power supply. Therefore, the traditional polarity reversal protection device must be designed for a high power loss accordingly.